B+ mounted integrated active rectifier electronics

ABSTRACT

A method of cooling electronics of an alternator includes mounting the electronics onto an electrically conductive chassis, and electrically connecting the chassis to positive DC output voltage (B+) of the alternator, whereby the chassis is electrically insulated from ground potential and conductively isolated from heat of the housing. An alternator includes a housing at ground potential, a chassis at B+ potential, and electronics mounted to the chassis, where the chassis is electrically insulated and conductively isolated from the housing. An electric machine includes a B+ chassis having an electronics mounting surface, having a convection surface, and defining an electrical bus for conducting a B+ potential. A chassis assembly has an insulator secured between a frame at ground potential and the B+ chassis.

BACKGROUND

The present invention is directed to improving efficiency andreliability of an electric generator and, more particularly, to reducingelectrical resistance while directing thermal transfer in an integratedsystem including rectifier electronics.

Alternators convert mechanical energy into electrical energy for avehicle. The rotor of an automotive alternator is typically driven by abelt and pulley system to rotate within stator windings coiled on alaminated iron frame. The magnetic field from the spinning rotor inducesan alternating voltage into the stator windings. The alternating voltage(AC) is typically then converted to a direct current (DC) voltage by arectifying circuit that outputs the DC voltage to one or more batteriesand to electrical devices of a vehicle.

A rectifying circuit may be formed using diodes, MOSFET devices, or byother structure. The rectifying circuit and associated controlcomponents may be located in an alternator housing.

Modern automotive alternators are generally required to supplyever-greater amounts of electrical current. For example, hybrid andelectric vehicles may use electricity instead of internal combustion fordriving the wheels, and an alternator may be combined with a starter ina mild hybrid configuration such as in a belt alternator starter (BAS)system. Other electrical loadings from air conditioning, electric powersteering, and various vehicle systems further increase the requiredalternator electrical generation capacity. As a result, efficiency ofautomotive alternators needs to be optimized. Efficiency is generallylimited by fan cooling loss, bearing loss, iron loss, copper loss, andthe voltage drop in the rectifier bridges. The use of permanent magnetsmay increase efficiency by providing field flux without relying on awound field that inherently creates ohmic losses. An alternator may havedual internal fans to improve operating efficiency and durability and toreduce heat-related failures. Many conventional alternator systems areaddressed to such concerns. However, additional improvements aredesirable.

Available space within a motor vehicle engine compartment is limited asmanufacturers strive to reduce the size of vehicles while maximizingpower and efficiency. With multiple components packed in a relativelysmall space, the heat generated by a number of devices increases thetemperature within the engine compartment. In addition, a tightly packedengine compartment may have limited space available for the flow ofcooling air to reduce component temperatures. Excessive enginecompartment temperatures may adversely affect device performance,including performance of the alternator.

Efficiency and reliability of an electrical generating device areaffected by many factors, including the total resistance of outputcircuitry and the construction methodology. Reducing electricalresistance of a rectification circuit and controlling the flow of heatprovides improvements in generator efficiency and reliability.

SUMMARY

It is therefore desirable to obviate the above-mentioned disadvantagesby providing an electric machine such as an alternator, and a method ofcooling such an electric machine.

According to an exemplary embodiment, a method of cooling electronics ofan alternator having a housing electrically at ground potential includesmounting the electronics onto an electrically conductive chassis, andelectrically connecting the chassis to positive DC output voltage (B+)of the alternator, where the chassis is electrically insulated fromground potential and conductively isolated from heat of the housing.

According to another exemplary embodiment, an alternator includes ahousing at ground potential, a chassis electrically connected topositive DC output voltage (B+) of the alternator, and electronicsmounted to the chassis, where the chassis is electrically insulated fromthe ground potential and conductively isolated from heat of the housing.

According to a further exemplary embodiment, an electric machineincludes a stator core having a plurality of phase coils wound thereon,and a B+ chassis having an electronics mounting surface, having aconvection surface, and defining an electrical bus for conducting a B+potential. Electronics are structured for inputting AC voltages from therespective phase coils and for rectifying such AC voltages into a DCvoltage defined between the B+ potential and a ground potential, theelectronics being directly mounted to the electronics mounting surface.The electric machine also includes a frame coupled to the groundpotential, and an insulator secured between the frame and the B+chassis.

The foregoing summary does not limit the invention, which is defined bythe attached claims. Similarly, neither the Title nor the Abstract is tobe taken as limiting in any way the scope of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The above-mentioned aspects of exemplary embodiments will become moreapparent and will be better understood by reference to the followingdescription of the embodiments taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a schematic view of an exemplary electric machine;

FIG. 2 is a simplified electrical schematic of an exemplary electronicscircuit for a three-phase alternator;

FIG. 3 is a top plan view of an exemplary MOSFET rectifier circuit for asingle phase;

FIG. 4 is a top plan view of an exemplary general layout forrectification and control electronics of a three phase alternator;

FIG. 5 is a partial perspective view of one axial end of an exemplaryalternator housing;

FIG. 6 is a top plan view of the heat exchange side of an electronicschassis assembly that includes an electronics chassis, according to anexemplary embodiment;

FIG. 7 is a perspective view of the heat exchange side of theelectronics chassis assembly of FIG. 6;

FIG. 8 is a perspective view of the electronics chassis assembly of FIG.6 being placed into position for securement to the alternator housing ofFIG. 5, according to an exemplary embodiment;

FIG. 9 is a perspective view of a ventilating insulator, according to anexemplary embodiment;

FIG. 10 is a partial perspective view of an electronics chassis assemblyplaced into position for securement to the alternator housing of FIG. 5,according to an exemplary embodiment;

FIG. 11 is a top plan view of a B+ electronics chassis assembly showingground, phase, and B+ potentials being fed to power electronics boardsand to a central control circuit, according to an exemplary embodiment;

FIG. 12 is a partial perspective view showing a welded bimetal phaselead before such structure is partially covered in a plastic over-mold,according to an exemplary embodiment;

FIG. 13 is a partial perspective view showing a cross-section through aB+ output stud and a B+ receiving portion, according to an exemplaryembodiment; and

FIG. 14 is a partial view showing a cross-section through a ground taband an aluminum phase bar, according to an exemplary embodiment.

Corresponding reference characters indicate corresponding or similarparts throughout the several views.

DETAILED DESCRIPTION

The embodiments described below are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Rather, theembodiments are chosen and described so that others skilled in the artmay appreciate and understand the principles and practices of theseteachings.

FIG. 1 is a schematic view of an exemplary electric machine 1 having astator 2 that includes stator windings 3 such as one or more coils. Anannular rotor body 4 may also contain windings and/or permanent magnetsand/or conductor bars such as those formed by a die-casting process.Rotor 4 includes an output shaft 5 supported by a front bearing assembly6 and a rear bearing assembly 7. Bearing assemblies 6, 7 are secured toa housing 8. Typically, stator 2 and rotor 4 are substantiallycylindrical in shape and are concentric with a central longitudinal axis9. Although rotor 4 is shown radially inward of stator 2, rotor 4 invarious embodiments may alternatively be formed radially outward ofstator 2. Electric machine 1 may be a motor/benerator or other device.In an exemplary embodiment, electric machine 1 may be an alternator.Housing 8 may have a plurality of longitudinally extending fins (notshown) formed to be spaced apart from one another on a housing externalsurface for dissipating heat produced in the stator windings 3. Anexternal electronics space 10 may be provided adjacent an axial end ofhousing 8 and/or an internal electronics space 11 may be provided withinhousing 8 for containing rectifying circuitry, control circuitry, andother associated components.

FIG. 2 is a simplified electrical schematic of an exemplary electronicscircuit 12 for a three-phase alternator 13. Alternator 13 outputsalternating current (AC) voltages at respective phase leads 14, 15, 16.Phase leads 14-16 are each connected to a separate half-bridge rectifierwithin a rectifier circuit 17 that converts the AC phase voltages into aDC voltage provided to a DC bus 18. In the illustrated embodiment, eachhalf-bridge includes a high-side MOSFET and a low-side MOSFET, wherebyphase lead 14 connects to the Source of high-side MOSFET circuit 19 andto the Drain of low-side MOSFET circuit 20, phase lead 15 connects tothe Source of high-side MOSFET circuit 21 and to the Drain of low-sideMOSFET circuit 22, and phase lead 16 connects to the Source of high-sideMOSFET circuit 23 and to the Drain of low-side MOSFET circuit 24. Invarious embodiments, any of MOSFET circuits 19-24 may be an N-channeldevice or a P-channel device. MOSFET circuits 19-24 typically include afree-wheeling diode as shown. Although MOSFET circuits 19-24 areillustrated as being single devices, each may include any number ofMOSFET devices. For example, each MOSFET circuit 19-24 may includeseveral MOSFET devices connected in parallel, whereby all Gate terminalsare connected, all Drain terminals are connected, and all Sourceterminals are connected together. In such a case, a higher currentcapacity may be obtained for each MOSFET circuit 19-24.

A control circuit 25 controls rectifier 17 and other devices, andincludes a control block 26 and MOSFET drivers 27. Control circuit 25may receive various signals from sensors (not shown), phase signals14-16, and control signals, and may transmit control and informationsignals for implementing various functions, including functions forcontrolling alternator operation. Control circuit 25 may be configuredto communicate with one or more remote device(s) such as amicrocontroller 28 that, in turn, is in communication with other remotedevices (not shown) via one or more analog or digital bus circuit(s) 29.Such communication may include transmitted/received control messages,architecture modifications such as software or firmware updates, errormonitoring, voltage and current regulation information, electricalloading information, profile information and control such as forimplementing dynamic control, and others. Since the operation of analternator, by itself may be simplified in various embodiments, controlcircuit 25 may be formed using analog control. For example, timingsensing may be obtained directly from the phase voltages. When morecomplicated controls are required, such control circuitry may includedigital devices. Any appropriate technology may be implemented forcontrol circuitry, including discrete devices, processor(s), and/orcombined circuitry such as application specific integrated circuit(s)(ASIC).

The operation and configuration of circuit 12 may be modified dependingupon the particular alternator application. For example, control circuit25 may be coupled to an external power supply, rectifier circuit 17 mayinclude any number of MOSFETs, diodes, and other components. The term“MOSFET” has become somewhat generic. For example, the previously metalgate material is now often a layer of polysilicon (polycrystallinesilicon). The term “enhancement mode” refers to the increase ofconductivity with increase in oxide field that adds carriers to thechannel, also referred to as the inversion layer. The channel cancontain electrons (called an nMOSFET or nMOS), or holes (called apMOSFET or pMOS), opposite in type to the substrate, so nMOS is madewith a p-type substrate, and pMOS with an n-type substrate. In adepletion mode MOSFET, the channel consists of carriers in a surfaceimpurity layer of opposite type to the substrate, and conductivity isdecreased by application of a field that depletes carriers from thissurface layer. As used herein, a MOSFET may also refer an insulated-gatefield-effect transistor (IGFET).

FIG. 3 is a top plan view of an exemplary MOSFET rectifier circuit 30for a single phase. Rectifier circuit 30 may be formed on a ceramicsubstrate 31 using a combination of technologies such as thick-film,wire bonding, semiconductor processes, and others. For example, MOSFETdevices may be separately formed as semiconductor chips using athin-film technology. Rectifier circuit 30 includes a low side formed asa generally rectangular thick-film island 32 using a conductive materialsuch as silver, gold, or other. Low side island 32 is electricallyconnected to the single phase at pads 33, 34 via respective bonded wiresets 35, 36. The number of individual bonded wires used in a givenconnection corresponds to the current carrying capacity thereof. Forexample, when bonded wire sets 35, 36 each contain eight wires, atypical current capacity may thereby be provided for a peak current ofapproximately 375 amperes. Individual bond wires in a typical embodimentmay be 0.015 to 0.020 inch aluminum, but any other gauge and type ofmaterial may alternatively be used.

Low side island 32 encloses MOSFETs 37-40 that are electricallyconnected in parallel with one another, whereby the four MOSFETs 37-40may substantially act as a single device (e.g., MOSFET device 20 of FIG.2) having an increased current capacity. When MOSFETs 37-40 areN-channel devices, the tops of such devices include respective Sourceterminals that are wire bonded as shown to ones of pads 41-43electrically at ground potential. The individual Gate terminals ofMOSFETs 37-40 are respectively electrically connected to a low side gatedrive conductor 44 with bonded wires 45-48. The respective Drainterminals of MOSFETs 37-40 are electrically connected to the phasevoltage of low side island 32 by conductors within respective thick filmregions 49 surrounding each MOSFET 37-40, or by other connection(s).

A high side island 50 encloses MOSFETs 51-54 electrically connected inparallel with one another, whereby the four MOSFETs 51-54 maysubstantially act as a single device (e.g., MOSFET device 19 of FIG. 2)having an increased current capacity. When MOSFETs 51-54 are N-channeldevices, the tops of such devices include respective Source terminalsthat are wire bonded via bonded wire sets 60-63 to low side island 32electrically at phase potential. The individual Gate terminals ofMOSFETs 51-54 are respectively electrically connected to a high sidegate drive conductor 55 with bonded wires 56-59. The respective Drainterminals of MOSFETs 51-54 may be electrically connected to the DC busvoltage (e.g., B+) potential of high side island 50 by conductors withinrespective thick film regions 64 surrounding each MOSFET 51-54, or byother connection(s). High side island 50 is electrically connected to aDC bus voltage (e.g., B+ potential) frame structure 65 by bonded wiresets 66, 67, where frame 65 may be formed to completely surroundrectifier circuit 30. Rectifier circuit 30 has a DC voltage terminal 68,a phase terminal 69, a ground terminal 70, a low side gate driveterminal 71, and a high side gate drive terminal 72, and such terminalsprovide convenient locations to provide corresponding input/output, suchas by jumpering.

FIG. 4 is a top plan view of an exemplary general layout forrectification and control electronics of a three phase alternator. Eachphase has a separate rectifier circuit 30. A control circuit 73 iselectrically connected to each of the three rectifier circuits 30 andcontrols all functions thereof. For convenience, terminals 68-72 (FIG.3) of each rectifier circuit 30 are now referred to collectively, foreach phase. For example, a rectifier circuit 30 for phase A hasterminals 74 that are jumpered by bonded wires to corresponding phase Aterminals 75 of control board 73, a rectifier circuit 30 for phase B hasterminals 76 that are jumpered by bonded wires to corresponding phase Bterminals 77 of control board 73, and a rectifier circuit 30 for phase Chas terminals 78 that are jumpered by bonded wires to correspondingphase C terminals 79 of control board 73. Control board 73 may have abasic configuration such as that shown by example as control circuit 25in FIG. 2, or it may have an alternative form. MOSFETs are typically notmounted directly to the ceramic substrates but are, instead, securedthereto with individual copper-invar-copper heat spreaders (not shown)having heights approximately 0.008 inch.

FIG. 5 is a partial perspective view of one axial end of an exemplaryalternator housing 80, typically formed of metal such as aluminum,steel, or other. Housing 80 is commonly at ground potential in manyautomotive applications. A B+ terminal 81 projects axially from aninterior mounting location and is structured for electrical connectionto a heavy gauge battery type cable (not shown) for outputting DCvoltage for charging one or more batteries (not shown) and for poweringvarious electrical loads. For example, B+ terminal 81 may be a threadedbolt. A voltage regulator 82, phase lead terminals 83, 84, 85, and othercomponents are formed or attached within housing 80 at the axial end 90.Such components may be located so that a cover and/or other structure,such as embodiments of an electronics chassis (described below), may beattached to a housing end surface 86 without contacting the axial endelectrical components. For example, axially extending threadedreceptacles 122 are provided at designed locations around thecircumference of housing end surface 86 and associated surroundingportions 123 of housing 80 are structurally adapted to accommodate suchreceptacles.

FIG. 6 is a top plan view of the heat exchange side of an electronicschassis assembly 106 that includes electronics chassis 87, according toan exemplary embodiment. Chassis 87 may be formed of aluminum or anotherelectrically conductive material. Aluminum is typically used because ofits light weight and adaptability to connection structure such as brazedor wire-bonded electrical joints. Electronics chassis 87, as describedfurther below, is connected to the DC voltage (B+) potential. An arrayof heat sink pins 89 are integrally formed to axially extend fromsurface 88 of aluminum electronics chassis 87. A center feature 91, suchas an indentation or a projection, may be provided to allow clearancefor an adjacent structure such as a hub or shaft assembly. B+ chassissurface 88 may include one or more B+ connection hole(s) 92 that may beformed for electrically connecting and structurally accommodatingassociated terminals (not shown), fasteners, wires, and the like. A B+bore 93 has a diameter slightly less than the diameter of B+ terminalpost 81 (FIG. 5), whereby post 81 may be interference fit into bore 93during assembly and thereby effect a B+ electrical connection. Such B+connection may also include a brazed or welded joint. B+ surface 88 mayhave consecutive outer edges 94-98 that are contiguous with one or moreelectrically insulating portion(s) that secure ground and phasepotentials in close proximity to edges 94-98. Aluminum ground tabs99-101, copper phase connections 102-104, and electronics chassis 87 areall joined together with an electrically insulating material such asplastic, whereby ground and multiple phase potentials are placed inproximity to the B+ potential of electronics chassis 87. Ground tabs99-101 each have mounting holes 105 for mounting electronics chassisassembly 106 to alternator housing 80 at corresponding threadedreceptacles (not shown) formed therein. Copper phase connections 102-104may be copper leads that are brazed or welded to aluminum terminal postshaving connection pads (described further below) and these copper toaluminum joints are each typically enclosed within respective plasticover mold portions 107-109.

FIG. 7 is a perspective view of the heat exchange side of electronicschassis assembly 106, according to an exemplary embodiment. An array ofheat sink pins 89 are integrally formed to axially extend from surface88 of aluminum electronics chassis 87. Heat sink pins 89 have variousheights that depend on the proximity of adjacent structure withinhousing 80. Since pins 89 and other portions of electronics chassis 87are at B+ potential, the heights of pins 110 are chosen to avoidshorting or otherwise contacting pins 110 with other components orground. A center recess 112 is provided to accommodate axial projectionof a hub or shaft assembly (not shown) when assembly 106 is mounted tohousing 80. Plastic over mold portion 113 includes over mold portions107-109. The B+ terminal post receiving portion 114 and the B+ terminalportion 115 may be formed at any appropriate locations along theperimeter of electronics chassis 87.

FIG. 8 is a perspective view of electronics chassis assembly 106 placedinto position for securement to alternator housing 80, according to anexemplary embodiment. Fasteners (not shown) such as screws or the likemay secure ground tabs 99-101 to threaded receptacles formed inrespective chassis support portions 116. Electronics mounting surface 88may be formed to include any number of machined portions for attachmentof B+ bonding wires thereto, may be configured in any appropriate shapefor fitment onto the axial end of housing 80, may be structured forcontaining any number of electronics devices such as ceramic substrates,and may contain any number of plastic over mold portion(s) forelectrically insulating phases, ground, B+ and any other electricpotential(s) from one another, and for providing structuralsupport/integrity.

FIG. 9 is a perspective view of a ventilating insulator 126, accordingto an exemplary embodiment. Ventilating insulator 126 is typicallyformed of thin plastic, and may be placed between an electronics chassis87, 125 (FIG. 10) and the surrounding portions at an axial end ofhousing 80. For example, ventilating insulator 126 may have respectivefirst and second raised portions 127, 128 formed in a center thereof,for spatially accommodating an underlying hub and/or shaft assembly ofan alternator. Ventilating insulator 126 may include openings 129, 130structured for accessing and/or spatially accommodating additionalcomponents such as phase terminal posts. Ventilation holes 131-134 areprovided to direct cooling air to pass therethrough and to flow in aparticular pattern to assist convection cooling of heat sink pins 110(FIG. 7). Additional features such as clips 135 and others, may beformed in ventilating insulator 126.

FIG. 10 is a partial perspective view of an electronics chassis assembly117 placed into position for securement to alternator housing 80,according to an exemplary embodiment. The shape of assembly 117substantially conforms to the combined, placed shape of three rectifierelectronics boards 30 and a ceramic board containing control circuit 73(FIG. 4). By such configuration, the amount of exposed aluminum ofaxially-outward-facing mounting surface 88, having B+ potential, may beminimized. In addition, the extra space may be provided for componentssuch as B+ post 81, phase terminals 83-85, voltage regulator 82, andothers, and may reduce or eliminate the need for further electricalinsulation between electronics chassis 117 and housing axial end surface90. For example, a plastic over mold member 118 may be formed with anaxially-extending wall that acts as a protective barrier for B+ surface31 and the electronics components mounted thereon, whereby suchelectronics and B+ surface 31 are axially recessed. Ground tabs 119-121may be integrally formed with a perimeter ground member 124. In such acase, plastic over mold member 118 separates perimeter ground member 124from the aluminum electronics chassis 125, whereby substantially theonly exposed B+potential of electronics chassis 125 is that which isformed as heat sink pins (e.g., FIG. 7) facing axially inward. Theadditional space provided by this configuration may allow more coolingair flow.

FIG. 11 is a top plan view of a B+ electronics chassis assembly 106showing ground, phase, and B+ potentials being fed to power electronicsboards 30 and central control circuit 73, according to an exemplaryembodiment. Electronics chassis 87 is at B+ potential. Surfaces 88, 137,138 are integral portions of chassis 87 and are, therefore, also at B+potential. Ground tabs 99-101 are integral with exposed ground surfaces139-141, all at ground potential. Phase connection pads 142, 143 arealuminum and are joined by brazing to copper phase connection 104. Phaseconnection pads 144, 145 are aluminum and are joined by brazing tocopper phase connection 103. Phase connection pads 146, 147 are aluminumand are joined by brazing to copper phase connection 102. Such brazedconnections are typically enclosed within plastic over mold 113. Groundsurfaces 139-141, phase connection pads 142-147, and electronicsmounting surface 88 of electronics chassis 87 are all substantiallycoplanar so that bonding wires from various portions of electronicsboards 30 and from control circuit 73 may be easily attached thereto. Inaddition, any associated attachment locations may be machined orotherwise prepared to provide reliable wire bonding surfaces. Forexample, electronics mounting surface 88 includes machined B+ wirebonding pads 147.

FIG. 12 is a partial perspective view showing a welded bimetal phaselead before such structure is partially covered in a plastic over-mold,according to an exemplary embodiment. The phase lead has a copper phaseconnection portion 102 (FIG. 11) and an aluminum phase manifoldstructure 148 joined together at a welded/brazed joint 149. Phase leadmanifold 148 is integrally formed to include phase pads 146, 147 thatmay have polished or machined surfaces suitable for wire bonding to anadjacent circuit 30 located on electronics mounting surface 88 ofchassis 87. Phase pads 146, 147 are interposed, such as by beinginterdigitated, between ground pads 150-152 of ground tab 101. The topsof pads 146, 147, 150-152 may be substantially coplanar with electronicschassis surface 88. In like manner, copper phase connection 103 and analuminum phase manifold structure 153 are joined together at awelded/brazed joint 154.

FIG. 13 is a partial view showing a cross-section through B+ output stud81 (FIG. 5) and B+ terminal post receiving portion 114 (FIG. 7),according to an exemplary embodiment. Ventilating insulator 126 (FIG. 9)is interposed between B+ electronics chassis 87 and surrounding metalstructure to prevent B+ chassis 87 from shorting thereto. One or morecover plate(s) 155 may be secured to an axial end of electric machine 1.Plastic over-mold 113 may be formed to electrically insulate and toprovide structural support for various components, as described above.B+ terminal post 81 may be set into and electrically insulated fromhousing 80 with a molded plastic insert 156, and the axially outwardportion of B+ terminal post 81 may be secured with a threaded lockingnut 157 to B+ terminal post receiving portion 114, thereby holding B+stud 81 securely in place.

FIG. 14 is a partial view showing a cross-section through a ground tab101 (FIG. 11) and an aluminum phase bar 148 (FIG. 12), according to anexemplary embodiment. Wire bonding pads 146, 150 are substantiallycoplanar with electronics mounting surface 88 of B+electronics chassis87. Heat sink pins 89 of B+ electronics chassis 87 may have differinglengths, depending on proximity of adjacent structure and on desiredcooling air flow through pins 89. Plastic over-mold 113 preventselectrical conduction between B+ chassis 87, phase lead manifold 148 andground tab 101.

As a result of utilizing a B+ electronics chassis that is electricallyand structurally isolated from the grounded main housing of an electricmachine, the electronics directly mounted on such B+ chassis arethermally decoupled from the housing. For example, since the B+chassismay be installed into the electric machine with little or no thermalconduction between the B+ chassis and the housing, the excessive heatoften generated by stator windings is not conducted into theelectronics; instead, a cooling air flow may enter the electric machineand be directed by the ventilating insulator and other structure tofirst cool the electronics and then proceed to cool the stator assemblywith the convection air flow. An aluminum B+ electronics chassis may beeasily formed with an electrical current capacity well in excess of adesigned peak current capacity, typically measured at the main B+terminal post. An upper limit for current through the electronics maydepend on physical limitations on the number and size of respectiveparallel feed-wire bonds from B+ and from ground. Multiple thick-filmpads and associated conductors may also be used for increasing currentcapacity. Suitable aluminum may be, for example, a type 50, 52, H32, 60,61, or other.

Each of the phase connections to the electronics may be segmented intotwo or more wire bonding pads, and a given phase connection may berouted around ground conductor(s) within the plastic over-mold. Byhaving a brazed joint within the plastic over-mold, a phase connectionprovides a copper end adapted for a solder joint and provides one ormore aluminum pads adapted for wire bonding. Typically, all plastic isformed in a single manufacturing step. A suitable plastic, for example,may be polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), orother, but nylon or any other relatively strong, electrically insulatingmaterial may be used in place of plastic over-mold material. PPS mayhave better flow characteristics for forming plastic in locations havingtight clearance space. Glass and/or fiber filler material may beincluded in the chosen plastic.

A reduced space and parts count, more efficient cooling, and an improvedassembly for alternator electronics are provided by the disclosedembodiments. For example, ground tabs of an electronics chassis assemblymay be kept very short and, therefore, such ground tabs may also berelatively thin because the associated electrical resistance is low andthe tabs do not need to carry electrical current for a long distance. Bymaintaining the electronics on coplanar substrates directly mounted tothe B+ chassis and by maintaining B+, phase, and ground connections tothe electronics on the same single plane, all intra-connections' lengthsmay be minimized and such connections may be formed simply by vibrationtype wire bonding. Short wire bonds have reduced electrical resistancecompared with traditional designs, and the disclosed embodiments alsoreduce the number of joints and interconnections compared withtraditional electric machines, further reducing electrical resistance.The B+ electronics chassis eliminates otherwise lengthy B+ conductorpaths and simplifies construction. For example, B+ of the electronicschassis is directly connected to the customer B+ terminal post withoutany additional conductor besides the traditional B+ post fastening nut(not shown).

The unitary heat sink pins of the B+ chassis improve temperature relatedperformance characteristics of an electric machine. Such heat sink pinsare thermally isolated from the heat of the adjacent housing as a resultof being structurally separated from the housing and other conductivesurfaces and as a result of the ventilating insulator placed between theelectronics heat sink and the axial end of the housing. By incorporatingthe heat sink into the electronics mounting chassis, surface area of theelectronics chassis being used for convective heat transfer, andcorresponding usage/accounting of the aluminum material, issubstantially increased. For example, the convection air flow may beprovided by one or more fans (not shown) located within the housingand/or externally of the housing, depending on the particular alternatorconfiguration. By the disclosed embodiments, the conductive heattransfer path between the electronics and the housing is eliminated.

While various embodiments incorporating the present invention have beendescribed in detail, further modifications and adaptations of theinvention may occur to those skilled in the art. However, it is to beexpressly understood that such modifications and adaptations are withinthe spirit and scope of the present invention.

What is claimed is:
 1. A method of cooling electronics of an alternator having a housing electrically at ground potential, comprising: mounting the electronics onto an electrically conductive chassis; and electrically connecting the chassis to positive DC output voltage (B+) of the alternator; whereby the chassis is electrically insulated from ground potential and conductively isolated from heat of the housing.
 2. The method of claim 1, further comprising providing the ground potential and a plurality of AC phase voltages to a plane that includes the electronics and the B+ voltage.
 3. The method of claim 2, further comprising forming intra-connections along the plane by wire bonding, from each of the ground potential, the chassis, and the plurality of phase voltages to the electronics.
 4. The method of claim 3, further comprising providing a plurality of wire bonding pads for the wire bonding.
 5. The method of claim 1, further comprising providing convection air flow that first cools the chassis and then cools the housing.
 6. An alternator, comprising: a housing at ground potential; a chassis electrically connected to positive DC output voltage (B+) of the alternator; and electronics mounted to the chassis; wherein the chassis is electrically insulated from the ground potential and conductively isolated from heat of the housing.
 7. The alternator of claim 6, further comprising a plurality of AC phase voltage terminals, wherein the ground potential and the plurality of phase terminals are disposed in a plane that includes the electronics and a surface of the chassis having the B+ voltage.
 8. The alternator of claim 7, further comprising intra-connections formed along the plane by wire bonding, from each of the ground potential, the chassis, and the plurality of phase voltages to the electronics.
 9. The alternator of claim 8, wherein the chassis has an axially outward facing surface along the plane.
 10. The alternator of claim 9, wherein the chassis has an axially inward facing surface with integrally-formed heat sink projections.
 11. The alternator of claim 10, wherein the heat sink projections include axially inward facing pins.
 12. An electric machine, comprising: a stator core having a plurality of phase coils wound thereon; a B+ chassis having an electronics mounting surface, having a convection surface, and defining an electrical bus for conducting a B+ potential; electronics structured for inputting AC voltages from the respective phase coils and for rectifying such AC voltages into a DC voltage defined between the B+ potential and a ground potential, the electronics directly mounted to the electronics mounting surface; a frame coupled to the ground potential; and an insulator secured between the frame and the B+ chassis.
 13. The electric machine of claim 12, wherein the B+ chassis includes a plurality of cooling pin fins projecting from the convection surface.
 14. The electric machine of claim 12, wherein the insulator is formed as a plastic over-mold.
 15. The electric machine of claim 14, further comprising a plurality of phase connection devices and at least one ground tab, each secured within the insulator.
 16. The electric machine of claim 12, wherein the electronics includes a plurality of rectifying MOSFET devices for each phase.
 17. The electric machine of claim 12, wherein the B+ chassis defines a single plane having a positive DC voltage bus, a plurality of phase voltage inputs, and ground potential.
 18. The electric machine of claim 12, further comprising a thermally conductive adhesive securing the electronics to the electronics mounting surface.
 19. The electric machine of claim 12, wherein the electronics include three ceramic power boards, and wherein the boards are mounted to the electronics mounting surface with a thermally conductive adhesive.
 20. The electric machine of claim 12, wherein all intra-connections of the electronics are wire bonded. 